Nutrient Assimilation in Southern Highbush Blueberry and Implications for the Field

Successful blueberry ( Vaccinium sp.) cultivation typically requires soils with low pH, high organic matter, readily available iron, and nitrogen (N) in the ammonium form. Growth of blueberry on typical mineral soils (higher pH, low organic matter) is reduced. Although soil pH effects on nutrient availability and uptake are known, it is unclear if the requirement for low soil pH in blueberry production is due to effects on nutrient availability/uptake or is a more direct effect of rhizosphere pH on root function. In addition, it is unclear if the requirement for high organic matter (soil amendments) is related directly to nutrient availability/uptake. Several studies have examined the use of rootstocks to increase soil adaptation of blueberry and some of these rootstocks have been found to increase plant vigor and yield. In particular, we have investigated whether sparkleberry ( Vaccinium arboreum )—a wild blueberry species that is adapted to high pH and low organic matter soils—could be used as a rootstock for commercial production of blueberry on mineral soils. Our work indicates that both nitrate (NO 3 − ) and iron (Fe) uptake and assimilation are greater in sparkleberry compared with southern highbush blueberry [SHB ( Vaccinium corymbosum interspecific hybrid)]. This is correlated with increased activity of nitrate reductase (NR) and iron chelate reductase, the rate limiting enzymes for NO 3 − and Fe acquisition, respectively. Field studies comparing growth and yield of own-rooted vs. grafted ‘Meadowlark’ and ‘Farthing’ SHB in amended vs. nonamended soils are ongoing. In general, own-rooted plants on amended soils exhibit greater growth than own-rooted on nonamended soils, while grafted plants in either soil system exhibit intermediate growth. Yields generally followed this pattern. Our preliminary results suggest that tolerance of SHB to mineral soils is greater when plants are grafted onto sparkleberry than when grown on their own roots. However, growth and yield of grafted plants grown under mineral soil conditions may not equal or exceed that of own-rooted plants grown under optimum soil conditions, at least in the first years after field planting. Longer term studies are necessary to fully evaluate the potential of using sparkleberry and other blueberry species as rootstocks for SHB and northern highbush blueberry ( V. corymbosum ).